(1) Field of Invention
This invention relates generally to the field of seismic prospecting and more particularly to three-component three-dimensional seismic data acquisition.
(2) Description of the Prior Art
In traditional methods of generating seismic data a straight line, referred to as a seismic shot line, is established on the terrain and seismic receivers are placed along the line and injections of acoustic energy into the subsurface are made at points (referred to as shot points) along the line. While the shot line is not necessary in seismic studies involving only compressional waves, it is necessary for shear wave seismic studies since the generation and detection of horizontal shear waves and vertical shear waves is always with respect to the vertical plane (referred to as the seismic plane) which includes the shot line.
An emerging area of seismic technology is the effort to produce three-dimensional images of the subsurface. Since the seismic data produced along a shot line provides two-dimensional images, the principle method for producing three-dimensional images in the past has been to make seismic measurements along a plurality of parallel shot lines and to combine the two-dimensional seismic data by extrapolating between the shot lines to provide the three-dimensional subsurface images. However, this method of generating three-dimensional seismic data on land surfaces has at least two drawbacks. First, a relatively large number of shot lines need to be made which involve the process of producing a large number of seismic energy injections into the ground which is generally very time consuming. Moreover, in some areas it is not possible to produce the desired parallel seismic shot lines due to geologic formations at the surface such as large rocks, deep depressions, and surface textures which are not well suited for seismic sources.
Therefore, it can be appreciated that a procedure for acquiring three-dimensional subsurface seismic data which does not require a relatively large number of seismic shot points and which is able to work around surface irregularities is highly desirable.